Methods of Forming Conductive Interconnects

ABSTRACT

The invention includes methods of electroless plating of nickel selectively on exposed conductive surfaces relative to exposed insulative surfaces. The electroless plating can utilize a bath which contains triethanolamine, maleic anhydride and at least one nickel salt.

TECHNICAL FIELD

The invention pertains to methods of forming conductive interconnects,and pertains to methods of depositing nickel.

BACKGROUND OF THE INVENTION

Semiconductor fabrication frequently involves formation of conductivematerials within openings, trenches or vias to form conductiveinterconnects. An exemplary prior art process for forming a conductiveinterconnect is described with reference to FIGS. 1 and 2.

Referring initially to FIG. 1, a semiconductor construction 10 is shownto comprise a semiconductor base 12 supporting an electricallyconductive node 14 and an electrically insulative material 16. Base 12can comprise, for example, a monocrystalline silicon wafer. Althoughbase 12 is shown having a homogeneous composition, it is to beunderstood that base 12 can comprise numerous layers and integratedcircuit devices (not shown). The combination of base 12 with structures14 and 16 can be referred to as a semiconductor substrate. To aid ininterpretation of the claims that follow, the terms “semiconductivesubstrate” and “semiconductor substrate” are defined to mean anyconstruction comprising semiconductive material, including, but notlimited to, bulk semiconductive materials such as a semiconductive wafer(either alone or in assemblies comprising other materials thereon), andsemiconductive material layers (either alone or in assemblies comprisingother materials). The term “substrate” refers to any supportingstructure, including, but not limited to, the semiconductive substratesdescribed above.

Electrically conductive node 14 can comprise any suitable material orcombination of materials, and can, for example, comprise, consistessentially of, or consist of one or both of copper and tungsten.

Electrically insulative material 16 can comprise any of numerousmaterials, and in some aspects will comprise, consist essentially of oneor both of silicon dioxide and silicon nitride. If material 16 comprisessilicon dioxide, such can be in either a substantially undoped form, orit can be in a doped form, such as, for example, borophosphosilicateglass (BPSG). Although material 16 is shown as a homogeneous material,it is to be understood that material 16 can comprise a plurality oflayers of differing electrically insulative compositions.

An opening 18 extends through material 16 to an upper surface 15 of node14. The opening 18 has a periphery comprising exposed sidewall surfaces17 of electrically insulative material 16, and the exposed upper surface15 of node 14. Opening 18 can have any of numerous shapes, and in someaspects can be a via or trench.

Referring next to FIG. 2, opening 18 is filled with conductive materialby first forming a thin adhesive liner 20 within the opening, andsubsequently forming a bulk conductive material 22 within the opening tofill the opening. The liner 20 can comprise a metal nitride (such as,for example, titanium nitride), and the bulk material can comprise ametal (such as, for example, tungsten). The liner 20 and bulk conductivematerial 22 can be formed by, for example, one or both of atomic layerdeposition and chemical vapor deposition. In subsequent processing (notshown) the liner material 20 and bulk conductive material 22 can beremoved from over insulative material 16 by, for example,chemical-mechanical polishing, while leaving the liner and conductivematerial within opening 18. The liner and conductive material remainingwithin the opening 18 can subsequently be utilized as a conductiveinterconnect for electrically connecting circuitry (not shown) to node14.

A difficulty encountered in forming the liner 20 and conductive material22 within opening 18 is that the deposited materials can pinch off a topof opening 18 during formation of the materials within the opening, andsuch can cause the opening to be less than uniformly filled with theconductive materials. This can decrease operability of an interconnectultimately formed in the opening, and in particularly problematic casescan destroy operability of an interconnect. A continuing goal ofsemiconductor processing is to increase packing density across a surfaceof a semiconductor wafer, and accordingly to reduce the widths (i.e.increase the critical dimensions) of openings associated withsemiconductor constructions. Difficulties associated with deposition ofconductive materials within openings are exacerbated as the openingsincrease in critical dimension. Accordingly, there has been a continuingeffort to develop new methods for forming conductive materials withinopenings.

One of the methods being developed for forming conductive materialswithin openings is to electroless plate the materials into the openingsin a manner such that the conductive materials grow upwardly from asurface of a conductive node at the bottom of the openings. The upwardgrowth of the electroless-plated materials can alleviate, and preferablyprevent, the above-discussed problem of the materials pinching off thetop of an opening before the materials have completely filled the bottomof the opening.

It has proven to be difficult, however, to develop methods whichselectively electroplate conductive materials on conductive surfacesrelative to insulative surfaces. If the plated materials grow oninsulative surfaces (such as, for example, the surfaces 17 of FIG. 1),the plated materials can pinch off the top of an opening before thematerials have filled the opening. Ideally, the plated materials wouldselectively grow on the conductive surface of an electrically conductivenode (such as, for example, the surface 15 of node 14 in FIG. 1), andthen continue to selectively grow on conductive surfaces relative toinsulative surfaces so that the plated material fills the opening byupward growth from conductive surfaces rather than by lateral orsideward growth from insulative surfaces.

For purposes of interpreting this disclosure and the claims that follow,a deposition process is considered to be “selective” for a first surfacerelative to a second surface if deposition occurs more rapidly in thefirst surface than the second surface, which can include, but is notlimited to, conditions in which the deposition occurs only on the firstsurface and not on the second surface (i.e., conditions in which thedeposition is 100% selective for the first surface relative to thesecond surface).

A conductive material which is commonly utilized in electroplatingprocesses is nickel. However, a problem in utilizing nickel to fillopenings (such as the opening 18 of FIG. 1) is that it can be difficultto electroless plate the nickel on a conductive surface of copper ortungsten (such as the surface 15 of node 14) without first activatingsuch conductive surface. The activation frequently comprises provisionof palladium onto the surface to provide loci for subsequent depositionof nickel during an electroless plating process. Unfortunately, theactivation conditions can also form loci on the exposed surfaces 17 ofinsulative material 16, and accordingly can result in electrolessplating of nickel along the lateral surfaces 17 of opening 18. Theplating of nickel on the lateral surfaces 17 can lead to lateral growthof the electroless-plated nickel across the opening, which can pinch offthe opening before the electroless-plated conductive material hasentirely filled the opening.

It is desired to develop new methods for electroless-plating ofmaterials within openings which alleviate, and preferably prevent, thevarious problems discussed above. It is further desired to developmethods for electroless plating which are selective for plating onconductive surfaces relative to insulative surfaces, and whichpreferably can be conducted without activation of the conductivesurfaces.

SUMMARY OF THE INVENTION

In one aspect, the invention includes a method of depositing nickel. Asemiconductor substrate is provided. The substrate has a surface of anelectrically conductive node, and also has a surface of an electricallyinsulative material. The surfaces of the conductive node and theelectrically insulative material are both exposed to an electrolessplating bath. The bath is utilized for selectively electroless platingnickel on the surface of the node relative to the surface of theelectrically insulative material. The plating bath containstriethanolamine, maleic anhydride and at least one nickel salt. Theplating bath can further include a reducing agent, such as, for example,dimethyl aminoborane (DMAB).

In one aspect, the invention includes of forming a conductiveinterconnect. A semiconductor substrate is provided. The substrate hasan electrically conductive node, an electrically insulative materialadjacent the node, and an opening extending through the insulativematerial to a surface of the node. A sidewall periphery of the openingcomprises an exposed surface of the electrically insulative material.Nickel is electroless plated within the opening to form the conductiveinterconnect within the opening. The electroless plating selectivelydeposits the nickel on the surface of the node relative to the exposedsurface of the electrically insulative material. The electroless platingcomprises provision of a bath within the opening, with such bathcontaining a nickel salt, a metal chelator, triethanolamine, a reducingagent and maleic anhydride.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a diagrammatic, cross-sectional view of a semiconductor waferfragment at a preliminary processing stage of a prior art process forforming a conductive interconnect.

FIG. 2 is a view of the FIG. 1 fragment shown at a prior art processingstage subsequent to that of FIG. 1.

FIG. 3 is a diagrammatic, cross-sectional view of a semiconductor waferfragment shown at a preliminary processing stage of an exemplary aspectof the present invention.

FIG. 4 is a view of the FIG. 3 wafer fragment shown at a processingstage subsequent to that of FIG. 3.

FIG. 5 is a view of the FIG. 3 wafer fragment shown at a processingstage subsequent to that of FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws “to promote the progressof science and useful arts” (Article 1, Section 8).

The invention includes a new electroless plating bath chemistry whichcan selectively plate nickel on materials comprising one or both ofcopper and tungsten relative to other materials. In particular aspects,the bath is utilized to selectively deposit nickel on an electricallyconductive surface relative to an electrically insulative surface, andis utilized without prior activation of the electrically conductivesurface. The selectivity of the plating conditions of the presentinvention for surfaces comprising, consisting essentially of, orconsisting of one or both of copper and tungsten relative toelectrically insulative surfaces can be very high, with the selectivityapproaching 100% (i.e., with the selectivity being such that electrolessplating occurs on the surfaces containing copper and/or tungsten whilenot occurring to a measurable extent on the electrically insulativesurfaces) in some aspects of the invention.

An exemplary aspect of the invention is described with reference toFIGS. 3-5. Referring initially to FIG. 3, a semiconductor construction10 is illustrated at a preliminary processing stage of an exemplarymethod of the invention. In describing construction 10, similarnumbering will be used as was utilized above in describing the prior artconstruction 1. Construction 10 comprises the base 12, electricallyinsulative material 16 and conductive node 14 described previously.Accordingly, base 12 can comprise a monocrystalline semiconductor wafertogether with various levels of integrated circuitry (not shown). Node14 can comprise, consist essentially of, or consist of one or both oftungsten and copper, and has an exposed uppermost surface 15 which canalso comprise, consist essentially of, or consist of one or both oftungsten and copper. Insulative material 16 can comprise any suitableelectrically insulative composition, or combination of compositions. Inparticular aspects, insulative material 16 will comprise, consistessentially of, or consist of one or both of silicon nitride and silicondioxide. The silicon dioxide can be either undoped, or can be in a dopedform, such as, for example, BPSG. The opening 18 extends throughinsulative material 16 to the upper surface 15 of electricallyconductive node 14. Opening 18 has a periphery which includes exposedlateral sidewall surfaces 17 of insulative material 16.

Insulative material 16 can be considered to be adjacent electricallyconductive node 14, in that insulative material 16 and conductivematerial 14 are closely proximate one another (and in the shown aspectof the invention in direct physical contact with one another) over thebase 12.

An electroless plating bath 50 is provided over construction 10 andwithin opening 18. Accordingly, surfaces 15 and 17 are exposed to theelectroless plating bath. Bath 50 is utilized for selectivelyelectroless plating nickel on the exposed surface 15 of node 14 relativeto the exposed surface 17 of insulative material 16.

FIG. 4 shows construction 10 after the electroless plating hasselectively plated a nickel-containing material 52 onto surface 15 ofnode 14 relative to insulative surfaces 17. Material 52 has an uppermostsurface 53. Once that material 52 covers node 14, the surface 53 becomesa new conductive node surface within the opening. The electrolessplating is preferably selective for electrically conductive surface 53relative to insulative surfaces 17 so that the nickel-containingmaterial continues growing upwardly within the opening even after node14 is completely covered by material 52. Accordingly, the electrolessplating is preferably selective for depositing nickel onto theconductive surface 53 comprising, consisting essentially of, orconsisting of nickel, relative to depositing nickel onto the insulativematerial surfaces 17.

One aspect of the invention is a recognition that a plating bathcontaining a combination of triethanolamine, maleic anhydride and atleast one nickel salt can selectively electroless plate nickel overelectrically conductive surfaces (such as surfaces comprising,consisting essentially of, or consisting of one or more of copper,nickel and tungsten) relative to electrically insulative surfaces.Accordingly, the plating bath can be utilized to uniformly fill anopening with nickel-containing material. A plating bath of the presentinvention can be utilized without activation of a surface comprising,consisting essentially of, or consisting of tungsten or copper, whichcan advantageously avoid the above-described prior art problemsassociated with utilization of activation conditions prior toelectroless plating.

In particular aspects, the electroless-plating bath is an aqueoussolution in which the triethanolamine is present to a concentration offrom about 35 grams per liter to about 80 grams per liter (with aconcentration of about 45 grams per liter being typical); the maleicanhydride is present to a concentration of from about 0.5 grams perliter to about 2.5 grams per liter (with a concentration of about 2grams per liter being typical); and the nickel salt is nickel sulfatepresent to a concentration of about 20 grams per liter to about 50 gramsper liter (with about 30 grams per liter being typical). It is notedthat the nickel salt can comprise other nickel salts such as, forexample, nickel chloride in addition to or alternatively to the nickelsulfate.

The various components of the plating bath are typically fully dissolvedin the bath solution, and accordingly the nickel salt is distributedamongst anions and cations within the bath. Accordingly, if the nickelsalt comprises nickel sulfate, the actual composition within the platingbath will be nickel cations and sulfate anions. Further, if other anionsbesides sulfate are present in the bath, there may be redistribution ofthe anions so that some of the nickel cations are paired with anionsother than sulfate. Regardless, the stoichiometry of nickel and sulfatewithin the bath will be equivalent to having the nickel sulfate saltwithin the bath. Accordingly, the bath can be referred to as containingthe nickel sulfate salt even though the bath actually contains nickelcations and sulfate anions. Throughout this disclosure and the claimsthat follow, a plating bath is referred to as containing various salts,and it is to be understood that such description includes aspects inwhich the salts are fully dissolved in a solution so that the cationsand anions of the salts are dispersed within the solution rather thanbeing in crystalline salt form.

The electroless plating bath can include numerous components in additionto the nickel salt, triethanolamine and maleic anhydride discussedabove. For instance, the plating bath can also include a metal chelatorand a reducing agent. An exemplary metal chelator is a salt ofethylenediaminetetraacetic acid (EDTA), such as, for example, thepotassium salt of EDTA. In particular aspects, the potassium salt ofEDTA is present in the plating bath to a concentration of from about 10grams per liter to about 25 grams per liter, with a typicalconcentration being about 15 grams per liter. The reducing agent can beselected from the group consisting of dimethyl aminoborane,hypophosphate, formaldehyde and one or more hydroborate salts. Forinstance, the reducing agent can be sodium hydroborate. If the reducingagent is dimethyl aminoborane, such can be present in the plating bathto a concentration of from about 6 grams per liter to about 15 grams perliter, with about 8 grams per liter being typical.

The various components of the plating bath can have numerous purposesand provide numerous advantages. For instance, the triethanolamine canaccelerate nickel deposition (plating) on electrically conductivesurfaces. As another example, the maleic anhydride can stabilize theplating bath solution so that the nickel remains dissolved in thesolution at the high concentration of nickel present. Without thestabilization of maleic anhydride, the nickel would tend to plate lessspecifically on the conductive materials relative to the insulativematerials, and accordingly various prior art problems could manifestfrom nickel non-specifically plating at the top of an opening before thenickel has fully and uniformly filled the opening.

An electroless plating solution of the present invention can be utilizedunder any suitable conditions. In particular aspects, the platingsolution is utilized while maintaining a pH of the solution at fromabout 7 to about 9.5 (with from about 8 to about 8.5 being typical), andwhile maintaining a temperature of the solution at from about 20° C. toabout 85° C. (with a temperature of about 60° C. being typical).Electroless plating can be conducted for any suitable time, with a timeof from about 1 minute to about 0.5 hours being typical.

Referring next to FIG. 5, such shows construction 10 after a sufficientamount of nickel-containing material 52 has been electroless platedwithin opening 18 to fill the opening, and after removal of bath 50(FIG. 3). In the shown aspect of the invention, the material 52 fullyand uniformly fills opening 18.

Material 52 forms a conductive interconnect extending through theopening to node 14, with such interconnect comprising, consistingessentially of, or consisting of nickel. The interconnect has aplanarized top surface. Such planarized surface can be formed by, forexample, chemical-mechanical polishing subsequent to the formation ofthe interconnect.

Circuitry 56 is diagrammatically illustrated in FIG. 5 as beingelectrically connected with the interconnect of material 52. Theinterconnect thus electrically connects node 14 with the circuitry 56.Persons of ordinary skill in the art will recognize that node 14 can beelectrically connected with various integrated circuit devicesassociated with semiconductor base 12, and that circuitry 56 cancorrespond to any of numerous structures desired to be connected withcircuit devices through electrical interconnects. Accordingly, theelectrical interconnect of material 52 can have broad application forincorporation into integrated circuitry fabrication.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1-43. (canceled) 44: A method of forming a conductive interconnect,comprising electroless plating nickel over an upper surface of anelectrically conductive node at the bottom of an opening through aninsulative material to form an electrically conductive interconnectwithin the opening, the electroless plating filling the opening from thebottom up and comprising utilization of a plating bath containing anickel salt, a metal chelator, triethanolamine, a reducing agent andmaleic anhydride. 45: The method of claim 44 wherein the electricallyconductive node is supported by a monocrystalline silicon base. 46: Themethod of claim 44 the upper surface of the electrically conductive nodecomprises one or both of copper and tungsten. 47: The method of claim 44the upper surface of the electrically conductive node comprises nickel.48: The method of claim 44 wherein the reducing agent is sodiumhydroborate. 49: The method of claim 44 wherein the metal chelator is asalt of ethylenediaminetetraacetic acid. 50: A method of forming aconductive interconnect, comprising: forming a construction having anelectrically conductive node over a monocrystalline silicon base, anelectrically insulative material adjacent the node, and an openingextending through the insulative material to a surface of the node, asidewall periphery of the opening comprising an exposed surface of theelectrically insulative material; and electroless plating nickel withinthe opening utilizing a plating bath containing a nickel salt, a metalchelator, triethanolamine, a reducing agent and maleic anhydride. 51:The method of claim 50 wherein the exposed surface of the electricallyinsulative material comprises one or both of silicon nitride and silicondioxide. 52: The method of claim 51 the surface of the electricallyconductive node comprises copper or tungsten. 53: The method of claim 51the surface of the electrically conductive node comprises nickel. 54:The method of claim 50 wherein the reducing agent is sodium hydroborate,and wherein the metal chelator is a salt of ethylenediaminetetraaceticacid. 55: A method of forming a conductive interconnect, comprising:electroless plating nickel over an electrically conductive node at thebottom of an opening through an electrically insulative material to forman electrically conductive interconnect within the opening, theelectroless plating filling the opening from the bottom up andcomprising utilization of a plating bath containing a nickel salt, ametal chelator, triethanolamine, a reducing agent and maleic anhydride;and wherein the electroless plating is conducted without prioractivation of the surface of the electrically conductive node. 56: Themethod of claim 55 wherein the surface of the electrically conductivenode comprises one or more both of copper and tungsten. 57: The methodof claim 55 wherein the electrically insulative material comprises oneor both of silicon nitride and silicon dioxide. 58: The method of claim55 wherein: the triethanolamine is present in the plating bath to aconcentration of from about 35 grams per liter to about 80 grams perliter; the maleic anhydride is present in the plating bath to aconcentration of from about 0.5 grams per liter to about 2.5 grams perliter; and the nickel salt is nickel chloride or nickel sulfate. 59: Themethod of claim 55 wherein the reducing agent is selected from the groupconsisting of dimethyl aminoborane, hypophosphate, formaldehyde and oneor more hydroborate salts. 60: The method of claim 55 wherein thereducing agent is dimethyl aminoborane or sodium hydroborate. 61: Themethod of claim 55 wherein the metal chelator is a salt ofethylenediaminetetraacetic acid. 62: The method of claim 55 wherein theelectroless plating occurs while the bath is maintained at a temperatureof from about 20° C. to about 85° C.